1. Field of Invention
The present invention generally relates to a method utilized in a wireless communication system and in a wireless communication device thereof, and more particularly to a method of handling the radio bearer resumption for the third Generation Partnership Project (3GPP) standard, a wireless communication device and a wireless communication system thereof.
2. Description of Prior Art
With the development of wireless communication systems, people can talk and transmit data via the wireless channel by using the wireless communication devices. Now, the 3GPP standard is evolving, and there are still some problems not solved.
Before the wireless communication device and the network backbone exchange the user data with each other, a control connection of the wireless communication device and the network backbone must be established. In the 3GPP standard, the control connection is the Radio Resource Control (RRC) connection, the wireless communication device is the User Equipment (UE), and the network backbone is the Universal Terrestrial Radio Access Network (UTRAN) used in the Wideband Code Division Multiple Access (WCDMA) system, or the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) used in the Long-Term Evolution (LTE) system.
Please see FIG. 1, FIG. 1 is a flow chart showing the RRC connection procedure of the wireless communication device and the network backbone. In the example, the wireless communication device is the UE, and the network backbone is E-UTRAN. In step S100, the UE sends the RRCConnectionRequest message. In step S102, after the E-UTRAN receives the RRCConnectionRequest message from a wireless channel, it sends the RRCConnectionSetup message or the RRCConnectionReject message. If the E-UTRAN rejects to establish the RRC connection, it sends the RRCConnectionReject message; otherwise, it sends the RRCConnectionSetup message. In step S104, the UE determines whether the RRCConnectionSetup message or the RRCConnectionReject message is received. If the RRCConnectionSetup message is received, step S106 is executed; if the RRCConnectionReject message is received, the RRC connection procedure is terminated. In step S106, the UE establishes the Signaling Radio Bearer 1 (SRB1). Then in step S108, after the UE receives the RRCConnectionSetup message, the UE sends the RRCConnectionSetupCommplete message. Accordingly, after the RRC connection procedure is done successfully, the SRB1 is established.
In the 3GPP standard, SRBs are defined as RBs which are used only for the transmission of RRC and Non-Access-Stratum (NAS) messages. More specifically, the following three SRBs are defined. The SRB0 is for RRC messages using the Common Control Channel (CCCH), which is one of the logical channels. The SRB1 is for RRC messages (which may include a piggybacked NAS message) as well as for NAS messages prior to the establishment of the SRB2, all using the Dedicated Control Channel (DCCH), which is another one of the logical channels. The SRB2 is for the NAS messages, using the DCCH, and the SRB2 has a lower-priority than the SRB1 and is always configured by the E-UTRAN after security activation. The other RBs are user Data Radio Bearers (DRBs) which are used for transmitting the user data.
However, the RRC connection sometimes must be reconfigured. With regard to the purpose for handover with the Universal Terrestrial Radio Access (E-UTRA), the RRC connection reconfiguration is required. The UE can measure the signal quality of the received signal thereof, and sends a measurement report to the E-UTRAN. The E-UTRAN receives the measurement report and determines whether the UE should handover according to the calculation of the measurement report. When the E-UTRAN determines the UE should handover within E-UTRA, the RRC connection reconfiguration procedure shall start.
The RRC connection reconfiguration procedure is controlled by the E-UTRAN, and may occur when the wireless communication device should handover. However, the RRC connection reconfiguration procedure is not limited in the handover case, and sometimes it may occur in the non-handover case. If the RRC connection reconfiguration procedure occurs in the handover case, the RRCConnectionReconfiguration message must include the mobilityControlInformation message, or the UE can not know it should handover.
Please see FIG. 2, FIG. 2 is a flow chart showing the RRC connection reconfiguration procedure of the wireless communication device and the network backbone when the wireless communication device should handover. In the example, the wireless communication device is the UE, and the network backbone is E-UTRAN. In step S200, the E-UTRAN sends the RRCConnectionReconfiguration message including the mobilityControlInformation message to the wireless channel. In step S202, the UE receives the RRCConnectionReconfiguration message including the mobilityControlInformation message from the wireless channel, and determines whether it is able to comply with the configuration included in the RRCConnectionReconfiguration message including the mobilityControlInformation message. If some parameter in the RRCConnectionReconfiguration message including the mobilityControlInformation message is invalid for the UE, the UE can not comply with the configuration included in the RRCConnectionReconfiguration message including the mobilityControlInformation message, and then step S216 is executed; otherwise, the UE can comply with the configuration included in the RRCConnectionReconfiguration message including the mobilityControlInformation message, and step S204 is executed.
In step S204, the UE switches to one target cell to achieve handover. If the eutra-CarrierFreq parameter is included in the mobilityControlInformation message, the UE considers the target cell to be one on the frequency indicated by the eutra-CarrierFreq with a physical cell identity indicated by the targetCellIdentity included in the mobilityControlInformation message; otherwise, the UE considers the target cell to be one on the current frequency with a physical cell identity indicated by the targetCellIdentity parameter included in the mobilityControlInformation message. In step S206, the UE re-establishes the Packet Data Convergence Protocol (PDCP) for all RBs that are established. In step S208, the UE re-establishes the Radio Link Control (RLC) for all RBs that are established.
It is noted that actions of steps S202-S208 upon the reception of the RRCConnectionReconfiguration message including the mobilityControlInformation message are part actions upon the reception of the RRCConnectionReconfiguration message including the mobilityControlInformation message. The other actions upon the reception of the RRCConnectionReconfiguration message including the mobilityControlInformation message, such as timer control, value setting, and so on, are specified in the 3GPP standard.
After the RRC connection reconfiguration of the UE is done, the UE sends the RRCConnectionReconfigurationComplete message to the wireless channel in step S210. Then the E-UTRAN receives the RRCConnectionReconfigurationComplete message from the wireless channel, and the RRC connection reconfiguration procedure is completed.
When the UE can not comply with the configuration included in the RRCConnectionReconfiguration message including the mobilityControlInformation message, the UE regards the reconfiguration procedure as failure, uses the configuration used prior to the reception of the RRCConnectionReconfiguration message, and then executes step S216. In step S216, the UE determines whether security has not been activated. If the security has not been activated, the UE performs the actions upon leaving RRC_CONNECTED with release cause ‘other’ in step S220; otherwise, the UE initiates the RRC connection re-establishment procedure in step S218. The details of step S220 and the security are specified in the 3GPP standard, and are not described herein again. The RRC connection re-establishment procedure is illustrated in the following description accompanied with FIG. 3.
In the RRC connection re-establishment procedure, the E-UTRAN shall reconfigure SRB1 and resume data (i.e. the RRCConnectionReestablishmentComplete message) transfer for this RB. Furthermore, the E-UTRAN shall re-activate the Access-Stratum (AS) security without changing algorithms. The RRC connection re-establishment procedure is initiated when one of the following conditions is met. One condition is that the radio link failure has been detected. The other conditions are the occurrences of the handover failure, the mobility from E-UTRA failure, the integrity check failure indication from lower layers, and the RRC connection reconfiguration failure. The occurrence of the handover failure means failing to handover within the intra-system, and the occurrence of the handover failure means failing to handover within the inter-system. The occurrence of the integrity check failure indication from lower layers means the calculated integrity being not same as the original or the default one.
Please see FIG. 3, FIG. 3 is a flow chart showing the RRC connection re-establishment procedure of the wireless communication device and the network backbone. In the example, the wireless communication device is the UE, and the network backbone is E-UTRAN. When the RRC connection re-establishment procedure is initiated, the UE suspends all RBs except the SRB0 in step S300. The SRB0 is used to transmit the RRCConnectionReestablishmentRequest message, and should not be suspended. In step S302, the UE performs cell selection in accordance with the cell selection process specified in the 3GPP standard. After the initiation of the RRC connection re-establishment procedure is done, the UE sends the RRCConnectionReestablishmentRequest message to a wireless channel by using the SRB0.
It is noted that actions of steps S300-304 upon the initiation of the RRC connection re-establishment procedure are part actions upon the initiation of the RRC connection re-establishment procedure. The other actions upon the initiation of the RRC connection re-establishment procedure, such as timer control, value setting, and so on, are specified in the 3GPP standard.
After the E-UTRAN receives the RRCConnectionReestablishmentRequest message from the wireless channel, it sends the RRCConnectionReestablishment message or the RRCConnectionReestablishmentReject message. If the E-UTRAN rejects to re-establish the RRC connection, it sends the RRCConnectionReestablishmentReject message; otherwise, it sends the RRCConnectionReestablishment message. In step S308, the UE determines whether the RRCConnectionReestablishment message or the RRCConnectionReestablishmentReject message is received. If the RRCConnectionReestablishment message is received, step S310 is executed; if the RRCConnectionReestablishmentReject message is received, step S318 is executed. When the RRCConnectionReestablishmentReject message is received, the UE performs the actions upon the actions upon moving from the RRC_CONNECTED state to the RRC_IDLE state, which are described in the 3GPP standard.
When the RRCConnectionReestablishment message is received, the UE re-establishes the PDCP for the SRB1 in step S310. In step S312, the UE re-establishes the RLC for the SRB1 in step S312. In step S314, the UE resumes the SRB1 after configuring it in accordance with the received radioResourceConfiguration information element included in the received RRCConnectionReestablishment message thereof. In step S316, the UE sends the RRCConnectionReestablishmentComplete message to a wireless channel via the SRB1. After the E-UTRAN receives the RRCConnectionReestablishmentComplete message, the RRC connection re-establishment procedure is completed.
It is noted that actions of steps S310-316 upon the reception of the RRCConnectionReestablishment message are part actions upon the reception of the RRCConnectionReestablishment. The other actions upon t the reception of the RRCConnectionReestablishment, such as timer control, value setting, and so on, are specified in the 3GPP standard.